Aminotransferases catalyze the transfer of an alpha-amino group from an alpha-amino acid to an alpha-keto acid. These enzymes, also called transaminases, generally funnel alpha-amino groups from a variety of amino acids to alpha-ketoglutarate for conversion into NH.sub.4.sup.+. Aspartate aminotransferase, one of the most important of these enzymes, catalyzes the transfer of the amino group of aspartate to alpha-ketoglutarate. In most vertebrates, NH.sub.4.sup.+ is converted into urea, and is excreted.
In terrestrial vertebrates, urea is synthesized by the urea cycle. One of the nitrogen atoms of the urea synthesized by this pathway is transferred from the amino acid aspartate. The other nitrogen atom and the carbon atom are derived from NH.sub.4.sup.+ and CO.sub.2. Ornithine is the carrier of these carbon and nitrogen atoms. Other reactions of the urea cycle lead to the synthesis of arginine from ornithine, an amino acid that occurs naturally as an intermediate in arginine biosynthesis. Alanine aminotransferase, which is also prevalent in mammalian tissue, catalyzes the transfer of the amino group of alanine to alpha-ketoglutarate which producing pyruvate and glutamate. Glutamate is then oxadatively deaminated, yielding NH.sub.4.sup.+ and regenerating alpha-ketoglutarate. (See, e.g., Stryer, L., 1988 (3rd ed.). Freeman.) High levels of NH.sub.4.sup.+ are toxic to humans. The synthesis of urea in the liver is the major route of removal of NH.sub.4.sup.+, and a complete block of any of the steps of the urea cycle is usually fatal, because there is no known alternative pathway for the synthesis of urea. Inherited disorders caused by a partial block of each of the urea cycle reactions have been diagnosed. The most common condition is an elevated level of NH.sub.4.sup.+ in the blood (hyperammonemia). A nearly total deficiency of any of the urea cycle enzymes results in coma or death shortly after birth.
The discovery of a new human beta-alanine-pyruvate aminotransferase and the polynucleotides encoding it satisfies a need in the art by providing new compositions which are useful in the diagnosis, treatment, and prevention of diseases associated with immune disorders and cancer.